1. Technical Field
Embodiments of the present disclosure relate generally to data transmission, and more specifically to a high speed voltage-mode driver supporting pre-emphasis.
2. Related Art
Driver circuits (drivers) are frequently used in data transmission. The inputs to such driver circuits are typically binary data, and the outputs are corresponding voltage or current signals of suitable signal strengths. The signal strengths of the output voltage or current may be designed to have values that ensure reliable and error free (or low error rate) transmission. In addition, driver circuits may be designed to have a controlled output impedance to match the impedance of a transmission path on which the outputs are transmitted. A voltage-mode driver is generally a driver circuit whose output is a voltage signal, the driver circuit being designed as a voltage source.
The output signals of such voltage-mode driver circuits, being typically of square wave shape (i.e., having sharp edges), contain high-frequency components, which may be attenuated by the transmission path, consequently resulting in errors in correct interpretation of the signal logic-levels at a receiver connected to receive the output signal. Pre-emphasis is a technique that is often used to address the problem noted above, and refers to increasing the amplitude of the output signal of a driver circuit immediately following a logic-level transition. The amplitude may subsequently be reduced to a desired steady-state level till another logic-level transition occurs. The increased amplitude (pre-emphasis, also termed feed-forward equalization or FFE) following logic-level transitions mitigates the adverse effect that a transmission path (which is typically band-limited) may have on the high frequency components of the output signal. Voltage-mode drivers with pre-emphasis may need to support high-speed operation, i.e., be capable of supporting high data-transmission rates, while also supporting operation at lower data-transmission rates.